Resolve IPFS-hosted resources

[gnarea]

To avoid unnecessary roundtrips, public gateways should resolve references to IPFS-hosted resources when delivering parcels via couriers (when the Internet is unavailable). This would require the public gateway to act as an IPFS node or have access to one.

Additionally, when the Internet is available, private gateways should have the option to resolve IPFS resource references via the public gateway or a local IPFS node. IPFS doesn't (yet) work on Android, so the Android Gateway would have to rely on the public gateway.

I'm tempted to keep write operations outside this issue to keep it simple, but would love feedback on whether to expand the scope.